Purification of gas



p 1961 J. H. KARCHMER ET AL 3,000,988

PURIFICATION OF GAS Filed Oct. 7, 1959 PURIFIED GAS 2| 24 7 ACID-GAS REMOVAL %L "7- ZONE l3 25 I2 A ---22 Q-cARBoNY1 SULFIDE REMOVAL H ZONE CARBONYL SULFIDE CONTAINING GAS L I I5 -'MAKE UP NaOH SOLUTION DISCARD NcOH SOLUTION INVENTORS. JEAN H. KARCHMER,

: BY MARJORIE W. EASTWOOD .0 k... a; g I p- 4 Patented Sept. 19, 1961 The present invention is directed to the purification of gas. More particularly, the invention is concerned with the purification of olefinic gases containing carbonyl sulfide. In its more specific aspects, the invention is concerned with removing carbonyl sulfide from acidic gases containing carbonyl sulfide. t

The present invention may be briefly described as a method for purifying gases such as olefins, which comprises contacting such gases containing carbonyl sulfide with soda-lime.

The soda-lime is preferably arranged in a bed in a contacting zone and may have a mesh size in the range from about 4 to about 20 mesh. A preferred mesh size may be in the range from about 8 to about 16 mesh.

The soda-lime may suitably be arranged in a bed sup ported on a carrier material. As examples of carrier material may be mentioned, kieselguhr, alumina, Floridin, diatomaceous earth, and the like. When the soda-lime is dispersed or carried by a carrier material, the carrier material and the soda-lime may have a mesh size within the range from about 4 to about 20 mesh, preferably in the range from about 8 to about 16 mesh.

Soda-lime is a mixture of hydrated lime and sodium hydroxide. The mixture may contain from about 0.5% to about 10% by weight of sodium hydroxide and about 90 to about 99.5% of hydrated lime. The mixture may suitably contain from about 0.1% to about by weight of water, with best results being obtained about 0.1% by weight of water although good results may be ob tained up to about 5% by weight of water.

Soda-lime employed in the practice of the present invention is described in an article by Arthur K. Lamb, Robert E. Wilson, and N. K. Chaney in the Journal of Industrial and Engineering Chemistry, Vol. 11, No. 5, page 420 and following entitled Gas Mask Absorbents.

In employing the soda-lime in the practice of the present invention, the soda-lime is preferably arranged as a bed in a contacting zone. However, the soda-lime may be employed as a suspension suspended in the gas which is to be purified. In the instances where the soda-lime is suspended in the gaseous material which is to be purified, the soda-lime may have particle diameters in the range from about 0.5 to about 100 microns with the majority of the particle sizes being in the range from about 40 to about 80 microns. In practicing the present invention. it will be preferred to purify the acidic gas containing carbonyl sulfide by first removing acidic materials such as hydrogen sulfide, sulphur dioxide, carbon dioxide, hydrogen cyanide, and the like, and to remove Water from the acidic material-free gas. Removal of, hydrogen sulfide and other acidic gases may easily be performed by scrubbing the carbonyl sulfide-containing gas in a scrubber containing an aqueous solution of sodium hydroxide. For example, an aqueous solution of sodium hydroxide having a Baum gravity in the range from about 1 to about 45 Baum may be used. A preferred Baum gravity may be about 20.

The moisture may suitably be removed from the acidic gas-free carbonyl sulfide-containing gas by contacting the acid gas-free material with a bed of activated alumina to remove moisture.

It is to be understood however that other means may be employed for removing acidic gases besides those mentioned. For example, it is well known to scrub acid gases with various scrubbing mediums and it is contemplated to be within the purview of the presentinvention to use other means besides caustic scrubbing to remove acid gases.

Likewise, it is considered within the purview of this in vention to use other means besides contacting with activated alumina to remove moisture from the gas. As exemplary thereof may be mentioned activated carbon and other adsorbent materials which will remove moisture from gases.

The present invention will be further illustrated by ing gas such as ethylene is introduced into an acid-gas removal zone 12. Acid-gas removal zone 12 is suitably an absorption tower containing bell cap plates or other suitable contacting means by way of which suitable contact is obtained between gases and liquids. Introduced into the top of contacting zone 12 by way of line 13 is an aqueous solution of sodium hydroxide. The descending sodium hydroxide solution contacts the ascending carbonyl sulfide containing-gas and substantially removes hydrogen sulfide, S0 hydrogen cyanide, and other acid gases therefrom. The used sodium hydroxide solution is withdrawn from zone 12 by way of line 14 and preferably is recycled at least in part byway of line 15 through line 13. 16 for control thereof and a pump 17. From time to time it may be desirable to withdraw a portion of the used sodium hydroxide solution and this may be accomplished by opening valve 18 in line 14. When used sodium hydroxide solution is discarded by opening valve 18, a like amount of fresh or makeup sodium hydroxide solution will be introduced by line 13 on manipulation of valve 19.

The carbonyl sulfide containing-gas substantially free of acidic material is Withdrawn from zone 12 by way of line 20 and introduced thereby into a drying zone 21 which suitably may contain a bed 22 of activated alumina to remove moisture therefrom. On the carbonyl sulfide containing-gas circulating upwardly through the bed 22 substantially all of the moisture is removed therefrom and an eifiuent gas is removed from zone 21 by way of line 23 and introduced thereby into a carbonyl sulfide removal zone 24 which suitably contains a bed 25 of sodalime. On circulation of the carbonyl sulfide containinggas through zone 24, substantially all of the carbonyl sulfide is removed from the gas and a purified gas product is withdrawn by way of line 26 for use as may be desired. Purified ethylene may be used as a refrigerant or it may be used in chemical manufacture for example in the production of polyethylene by polymerization.

In order to illustrate the invention further, a number of runs were performed in which an ethylene gas containing 46 parts per million of carbonyl sulfide and 28 parts per million of acetylene was passed at a rate of 150 milliliters per minute through U-tubes in series having a combined volume of milliliters and containing soda-lime. All of the carbonyl sulfide was removed with no apparent change in the acetylene content. The rate at which the ethylene gas Was charged to the U-tubes corresponds to a space velocity of v./v./hr. which is a practical plant operation.

In another operation as a gas rate of 800 milliliters per minute, appreciable amounts of the carbonyl sulfide pass through the U-tubes.

Another series of runs were made in which a gaseous blend containing a high concentration of carbonyl sulfide It is to be noted that line 15 contains a valve" and ethylene was passed through a bed of soda-lime. Frequent analyses of the efiiuent gas were made to determine when the column or bed became saturated and permitted highconcentration of 'carbonyl sulfideto pass 4 removing carbonyl sulfide by contacting same with sodalime.

The nature and objects of the present invention having been completely described and illustrated, what we wish through the bed. The results of theseoperations are 5 to clan? as new and useful and to secure by Letters shownin thefollowing-table which gives the carbonyl sul- Patent 18: th f fide concentration-of the inlet gas and exit-gas, the weight A z if. i an i? gas .f izfi and volume of the absorbent material, and the rate of car l Su 1C compnses K1011 6 mg sai gas. -W1

fl F th d t th t 1 ht f soda-lime containing from about 90% to about-99.5% ese 3 a 6 ac 10 by weight of hydrated lime and from about 0.5% to-about bonyl sulfideretained on the absorbent material and the 10% by Weight of Sodium hydroxide, the hydrated lime weight of carbonyl sulfide retained per unit weight of Containing f abqut 0.1% to about 59% by weight f absorbent were calculated. water.

Absorbent Test Gas In Gas Out COS Retained Cone. Rate, Space Ve- Cone. Wt.. per- -Descriptlon Wt.,g. COS, ml./ 10city,m1./ Volume, COS, Wt., g. cent of p.p.m. min. mL/hr. liters p.p.m. Absorbwt.) (wt.) ent 11. 23 3.0 0. 208 i I 13. 45 1.2 0.254 816 n1esh,.5.2%HiO 25.9(33 m1.).-. 16,900 106 193 16.66 5.2 0.315 17. 87 19.0 0. 33s 20. 00 74.8 0.379 10.43 7.5 0.197 a aa a a 2 222 f6 03% 2320001111.)... 10,000 100 ,107 31169 017 01599 34.72 0.4 0. 050 38.82 0.4 0.734 40. 55 0.8 0. 70s 43.19 7.1 0.816 45.21 27.3 0.855

From the data shown in the foregoing table, it will be 2 A. method in accordance with claim in which the clear that the soda-lime is a very good absorption mategas is ethylene. rial. .It is to be noted that the first operation absorbs 3. A method in accordance with claim 1 in which the 1.46% of its weight while in the second operation the gas, is dry. and free of acidic material. soda-lime absorbs 3.02 weight percent. The difierences 40 4. A method in accordance with claim I- in which the between the two absorbent materials are the particle size soda-lime is arranged in a bed. and the moisture content. The second operation with 5. A method in accordance with claim 1 in which ,the the lower moisture content (0.94%) was more efiicient soda-lime is supported on a carrier. despite the fact that its particle size was larger (4 to 8 6. A method in accordance with claim 1 in which the mesh) than the other material whose particle size was soda-lime is in the form of particles having a mesh size 8 to 16 mesh. and whose moisture content was 5.2 weight within the range from 4 to about 20 mesh. percent. "From these data, it will be clear that the mois- 7. A method for purifying an olefinic. gas containing ture content within the range given and the, mesh size of carbonyl sulfide, water, and acidic material which comthe) P ticles: may avean app e effect 011 the prises removing water and acidic material from said gas amount of the Carb Y whlch-may be b d and then contacting said water and acidic-material free by'ithfi 'P P i i' gas with soda-lime containing from about 90% to about 'Pmsent mvenuon' 'apphcable to vanous gage-S 99.5% by weight of hydrated lime and from about 0.5% Carbonyl Sulfidei g i i' i 'g i to 10% by weight of sodium hydroxide, the, hydrated lime finslandfne dwkyfinsPmtalmng car FR 1 K 6 containing from about 0.1% to about 5.0% by weight of substantially purified mcaccordance with the practice of water the present invention. As exemplary of the gases which may be employed and Purified in accordance with the 8. A method in accordance with claim 7 m which the practice of the present invention, may be mentioned the gas 15 ethylene' h following: light gases obtained from the catalytic crack- In accordance wlth claim 7 m w ing' of petroleum whose carbonyl sulfide content may be the s 15 hy 80'p.p.m.; ethylene fractionwhich may contain 50 p.p.m. COS. References Cited in the file of this patent The present invention is quite advantageous and useful UNITED STATES PATENTS in that heretofore it was not possible practically to remove carbonyl sulfide from impure gases containing it '.43(),312 Amend et al. Aug. 9, 1892 in that expensive and lengthy purification procedures 2,146,353 Rosebaugh Feb. 7, 1939 were necessary. It is. clear that a new and substantially 2,431,300 E i Sept. 6, 19.49

improved and, useful process, has been developed for l; l I 

1. A METHOD FOR PURIFYING AN OLEFINIC GAS CONTAINING CARBONYL SULFIDE WHICH COMPRISES CONTACTING SAID GAS WITH SODA-LIME CONTAINING FROM ABOUT 90% TO ABOUT 99.5% BY WEIGHT OF HYDRATED LIME AND FROM ABOUT 0.5% TO ABOUT 10% BY WEIGHT OF SODIUM HYDROXIDE, THE HYDRATED LIME CONTAINING FROM ABOUT 0.1% TO ABOUT 5.0% BY WEIGHT WATER. 